Air purification traditionally involved the use of a HEPA filter, ionizer, or electrostatic precipitator to remove particulate matter and airborne bacteria from the air. To reduce gas-phase pollutants, adsorbent materials including activated carbons and molecular sieves may be used. Adsorption is only effective at the early stage and efficiency is gradually reduced because of the eventual saturation of the adsorbent materials. Using adsorbent materials is not environmental friendly because it requires frequently replacement and merely transfers gas-phase pollutants into particle-phase pollutants.
Ozone generators for oxidation of gases pollutants may be used. Low level ozone generated by the ozone generators is ineffective for air purification, while high level ozone is harmful to human beings. The atmospheric lifetime of tropospheric ozone is about twenty two days. To reduce the lifespan of ozone, ozone or an oxidation reagent is combined with an adsorbent. The adsorbent acts as a confined media for the reaction to take place.
CN 1625675A discloses the use of an oxidizing agent and zeolite. The pollutant first passes through an oxidizing generator before entry into a molecular sieve housing the molecules. The purification process is ineffective because oxidation of the pollutant is too slow in a confined space such as the nanopores/micropores of zeolite and molecular sieve even if it contains an active site for a reaction. This is because when the reactant enters the pores, it is at its lowest energy level stage. In other words, the reactant is too stable to start and initiate any reaction. Furthermore, the pore volume of the zeolite and molecular sieve are a constant size throughout the entire reaction. Therefore smaller sized harmful intermediates are not held longer in the pore and are released to the environment in the middle of the reaction.
U.S. Pat. No. 5,835,840 discloses a method of air purification using photo catalytic oxidation on a surface of titanium oxides. A catalyst such as titanium dioxide is fixed on a matrix or on the surface of a duct such that ultraviolet light is incident on the catalyst as air moves over it. However, photo catalytic oxidation of a pollutant over a surface is too slow and not feasible for high air flow. High air flow may be achieved by using a long air duct with an ultraviolet irradiation system and controlling the rate of air flow. The system design is limited because it requires direct irradiation by the ultraviolet irradiation system onto the surface of the catalyst. Using a long air duct for the ultraviolet irradiation system increases the bulkiness of the system and does not permit a compact design. The system is unable to handle high level contaminant gases.